The traditional calibration approach in radio astronomy is the “sky-based" calibration approach. In this method, a sky model is used as a prior and simulated through the instrument model to obtain a set of visibility models. This model becomes equivalent to the “true" visibility, iteratively solving for the gains until the solutions converge. However, the sky model constructed for sky-based calibration may have mismodelled or missing sources, resulting in imperfect calibration solutions. These imperfections affect the observational data sets targeting the EoR and make signal detection difficult (see, for example, [1]}, [2]}, [3]}). There is another calibration approach being explored for calibrating interferometric data for sensitive observations. This is known as the redundant calibration approach [4]}, [5]}, and works for arrays like HERA, which have highly regular layouts with many redundant baselines. The redundant calibration method adopts a prior that the actual visibility of the redundant baselines is equal. Thus instead of modeling the true sky visibilities, this method solves for both them along with the gains. Since arrays with highly regular layouts have more measured visibilities than unique baselines, the system is overdetermined despite leaving the true visibility as free parameters. However, the redundant approach works if and only if the array layout is highly regular and has perfect redundancy with identical primary beams. In the absence of perfect redundancy, calibration using this approach can also adversely affect data analysis for sensitive observations.
